Suspended lighting fixtures employing shaped light guide illumination devices

ABSTRACT

A suspended lighting fixture for direct/indirect lighting having a broad light emitting surface and including a thin curved sheet of an optically transmissive material, an LED strip optically coupled to a light input edge of the curved sheet, one or more suspension elements, an elongated heat dissipating structural element longitudinally extending along the light input edge, and an opaque elongated housing at least partially enclosing the LED strip. The curved sheet may include forward-deflecting or forward-scattering elements distributed over an area of the curved sheet according to a two-dimensional pattern and configured to extract light from one location of the sheet and direct the extracted light toward a second location of the sheet.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 15/793,755,filed on Oct. 25, 2017, and claims priority from U.S. provisionalapplication Ser. No. 62/412,596 filed on Oct. 25, 2016, the disclosureof which is incorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

Not Applicable

NOTICE OF MATERIAL SUBJECT TO COPYRIGHT PROTECTION

A portion of the material in this patent document is subject tocopyright protection under the copyright laws of the United States andof other countries. The owner of the copyright rights has no objectionto the facsimile reproduction by anyone of the patent document or thepatent disclosure, as it appears in the United States Patent andTrademark Office publicly available file or records, but otherwisereserves all copyright rights whatsoever. The copyright owner does nothereby waive any of its rights to have this patent document maintainedin secrecy, including without limitation its rights pursuant to 37C.F.R. § 1.14.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to illumination devices that employ lightemitting diodes (LEDs) and sheet-form light guiding substrates. Moreparticularly, this invention relates to broad-area edge-lit LEDillumination panels. Embodiments described herein also relate to systemsthat incorporate such broad-area edge-lit LED illumination panels, suchas for example, lighting fixtures or luminaires, backlights, illuminatedsigns or displays, traffic signs, automotive lights, and the like.Embodiments described herein further relate to methods for formingcurved broad-area edge-lit LED illumination devices.

2. Description of Background Art

Conventionally, edge-lit illumination panels employ a planar light guideconfigured to transmit light in response to an optical transmission anda total internal reflection (TIR) and a light source optically coupledto an edge of the light guide. The light source is commonly representedby a linear fluorescent lamp or a strip of interconnected LEDs. Thelight guide typically includes light extracting elements distributedover the surface of the light guide which suppress TIR and cause thelight guide to emit light from its broad-area surface. The conventionaledge-lit illumination systems may exhibit certain limitations such asdifficulty to control angular distribution.

BRIEF SUMMARY OF THE INVENTION

Certain aspects of embodiments disclosed herein by way of example aresummarized in this Section. These aspects are not intended to limit thescope of any invention disclosed and/or claimed herein in any way andare presented merely to provide the reader with a brief summary ofcertain forms an invention disclosed and/or claimed herein might take.It should be understood that any invention disclosed and/or claimedherein may encompass a variety of aspects that may not be set forthbelow.

According to one embodiment, a shaped illumination device is exemplifiedby a flexible sheet of an optically transmissive material and a LEDsource optically coupled to an edge of the flexible sheet. The flexiblesheet has at least one curvature about an axis and defines a concavebroad-area surface, an opposing convex broad-area surface extendingparallel to said concave broad-area surface, a first edge, and anopposing second edge. The flexible sheet further includes a plurality oflight extraction elements formed in or on a broad-area surface of theflexible sheet. According to different implementations, the lightextraction elements may be formed in the concave surface of the flexiblesheet, in the convex surface of the flexible sheet or in both opposingsurfaces of the flexible sheet. The light extraction elements may beformed by discrete surface relief features distributed over an area ofthe flexible sheet according to a predefined two-dimensional pattern andconfigured for forward-deflecting or forward-scattering operation suchthat light extracted at one location of the flexible sheet can bereceived and re-emitted at another location of the flexible sheet.

According to one embodiment, a method of making a curved edge-litillumination device, consistent with the present invention, includesproviding a plurality of LEDs, a flexible sheet of an opticallytransmissive material, and a sheet of a reflective material. The methodfurther includes steps of forming light extracting features in theflexible sheet, bending the flexible sheet and the sheet of a reflectivematerial to a curved shape, positioning the sheet of a reflectivematerial adjacent to a convex surface of the flexible sheet, opticalcoupling the plurality of LEDs to an edge of the flexible sheet; andpartially enclosing the plurality of LEDs into an opaque housing.

Various implementations and refinements of the features noted above mayexist in relation to various aspects of the present inventionindividually or in any combination. Further features, aspects andelements of the invention will be brought out in the following portionsof the specification, wherein the detailed description is for thepurpose of fully disclosing preferred embodiments of the inventionwithout placing limitations thereon.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

The invention will be more fully understood by reference to thefollowing drawings which are for illustrative purposes only:

FIG. 1 is a schematic perspective view of a shaped light guideillumination device, according to at least one embodiment of the presentinvention.

FIG. 2 is a schematic section view and raytracing of a shaped lightguide illumination device, according to at least one embodiment of thepresent invention.

FIG. 3 is a schematic section view of a shaped light guide illuminationdevice, illustrating a bend angle and an emission cutoff angle,according to at least one embodiment of the present invention.

FIG. 4 is a schematic section view and raytracing of a shaped lightguide illumination device, showing a curved and tapered light guide,according to at least one embodiment of the present invention.

FIG. 5 is a schematic section view and raytracing of a shaped lightguide illumination device portion, showing forward-scattering surfacerelief features formed in convex and concave surfaces, according to atleast one embodiment of the present invention.

FIG. 6 is a schematic close-up section view of an individualforward-scattering light extraction element formed on a surface of alight guide and having a curved profile of a top surface, according toat least one embodiment of the present invention.

FIG. 7 is a schematic close-up section view of an individualforward-scattering light extraction element having a lower thicknesscompared to FIG. 6, according to at least one embodiment of the presentinvention.

FIG. 8 is a schematic close-up section view of an individualforward-scattering light extraction element having a rounded “hat”-typeshape, according to at least one embodiment of the present invention.

FIG. 9 is a schematic close-up section view of an individualforward-scattering light extraction element having a lower thicknesscompared to FIG. 8, according to at least one embodiment of the presentinvention.

FIG. 10 is a schematic close-up section view of an individualforward-scattering light extraction element having an irregular profileof a top surface, according to at least one embodiment of the presentinvention.

FIG. 11 is a schematic section view and raytracing of a light guideportion, showing forward-deflecting light extraction elements configuredto provide an asymmetric angular distribution of emitted light,according to at least one embodiment of the present invention.

FIG. 12 is a schematic section view and raytracing of a light guideportion, showing forward-deflecting light extraction elements configuredto provide an asymmetric angular distribution of emitted light in adifferent mode of operation, according to at least one embodiment of thepresent invention.

FIG. 13 is a schematic section view and raytracing of a light inputportion of a shaped light guide illumination device, showing a layer ofan index matched material disposed between a light emitting aperture ofa light emitting diode and a light input edge of a light guide,according to at least one embodiment of the present invention.

FIG. 14 is a schematic graph illustrating an angular distribution of asurface luminance of a light guide.

FIG. 15 is a schematic section view of a shaped light guide illuminationdevice, showing LED sources coupled to opposing edges of a light guide,according to at least one embodiment of the present invention.

FIG. 16 is a schematic section view of a shaped light guide illuminationdevice, showing a bend angle of about 90°, according to at least oneembodiment of the present invention.

FIG. 17 is a schematic section view of a shaped light guide illuminationdevice having a variable curvature, according to at least one embodimentof the present invention.

FIG. 18 is a schematic section view of a shaped light guide illuminationdevice having a substantially planar section adjacent to a light inputarea, according to at least one embodiment of the present invention.

FIG. 19 is a schematic section view of a shaped light guide illuminationdevice formed by two symmetrical sections, according to at least oneembodiment of the present invention.

FIG. 20 is a schematic perspective view of a suspended lighting fixtureemploying a shaped light guide illumination device, according to atleast one embodiment of the present invention.

FIG. 21 is a schematic section view of a suspended lighting fixtureemploying a shaped light guide illumination device having twosymmetrical sections, according to at least one embodiment of thepresent invention.

FIG. 22 is a schematic top view of a suspended lighting fixtureemploying a shaped light guide illumination device in a symmetricconfiguration, according to at least one embodiment of the presentinvention.

FIG. 23 is a schematic bottom view of a suspended lighting fixtureemploying a shaped light guide illumination device in a symmetricconfiguration, according to at least one embodiment of the presentinvention.

FIG. 24 is a schematic section view of a wall-mounted lighting fixtureemploying a shaped light guide illumination device in an asymmetricconfiguration, according to at least one embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Referring more specifically to the drawings, for illustrative purposesthe present invention is embodied in the system generally shown in thepreceding figures. It will be appreciated that the system may vary as toconfiguration and as to details of the parts without departing from thebasic concepts as disclosed herein. Furthermore, elements represented inone embodiment as taught herein are applicable without limitation toother embodiments taught herein, and in combination with thoseembodiments and what is known in the art.

A wide range of applications exists for the present invention inrelation to the collection and distribution of electromagnetic radiantenergy, such as light, in a broad spectrum or any suitable spectralbands or domains. Therefore, for the sake of simplicity of expression,without limiting generality of this invention, the term “light” will beused herein although the general terms “electromagnetic energy”,“electromagnetic radiation”, “radiant energy” or exemplary terms like“visible light”, “infrared light”, or “ultraviolet light” would also beappropriate.

It is also noted that terms such as “top”, “bottom”, “side”, “front” and“back” and similar directional terms are used herein with reference tothe orientation of the Figures being described and should not beregarded as limiting this invention in any way. It should be understoodthat different elements of embodiments of the present invention can bepositioned in a number of different orientations without departing fromthe scope of the present invention.

Various embodiments of the invention are directed to shaped light guideillumination devices and systems that employ an edge-lit light guidingsheet which is curved about at least one axis. For example, such curvedlight guiding sheet may be formed into the shape of a partialcylindrical trough with an arc-shaped transversal cross-section. Thetrough may have a transversal cross-sectional profile that can beapproximated by a portion of a conical section (e.g., a circle, anellipse, a parabola, or a hyperbola). The trough may have a constant ofvariable radius of curvature across its surface and may further haveplanar sections.

The light guide may me formed by a rigid sheet or slab of an opticallytransmissive, dielectric material, such as glass, PMMA or polycarbonate,for example. The light guide may also be formed by a relative thin sheetof the transmissive material that is flexible. The term “flexible”, asapplied to sheet-form structures (including flexible sheet-formsubstrates and/or layers), is generally directed to mean that suchstructures are capable of being noticeably flexed or bent with relativeease without breaking. It is noted that, while flexible sheet-formstructures are in contrast to the ones that are rigid or unbending, thematerial of a sheet-form structure does not need to be soft or pliablein order to make such sheet-form structure flexible. Accordingly, theterm “flexible” is directed to also include semi-rigid structures andstructures that are formed by relatively hard, rigid materials such asmetals, glass or rigid plastics, when such structures have sufficientlylow thickness compared to at least one their major dimension (e.g.,length or width) and allow for noticeable flexing without breaking.

The present invention will now be described by way of example withreference to the accompanying drawings.

FIG. 1 schematically shows an embodiment of a shaped edge-lit lightguide illumination device 900 having a rectangular sheet-formconfiguration and at least one curvature about an axis. Shapedillumination device 900 includes a curved light guide 4, an elongated,linear light source 10, a concave back reflector 30, and a plurality oflight extraction elements 6 distributed over a wide area of light guide4.

Light guide 4 is formed by a flexible rectangular sheet of highlytransmissive material. The flexible sheet is bent to a curved shape soit defines a concave broad-area surface 20 and an opposing convexbroad-area surface 40 extending parallel to surface 20. The flexiblesheet further defines four edges 12, 14, 16, and 18 connecting theopposing broad-area surfaces and flanking the solid, transparent body ofthe light guide. Concave broad-area surface 20 is configured for lightoutput and may further be configured for light input. Opposing convexbroad-area surface 40 extends parallel to surface 20 and is configuredfor both light input and output.

Edge 12 is configured for light input. Light guide 4 is configured toguide light from light input edge 12 to opposing edge 14 in response tooptical transmission and reflection from opposing broad-area surfaces 20and 40 by means of TIR. Light guide 4 is gently curved about an axisthat is parallel to light input edge 12 and perpendicular to a directionof the intended light propagation in the light guide. Similarly,reflector 30 may be formed from a flexible sheet-form material andcurved to the same shape as light guide 4.

The curved shape of light guide 4 may be characterized by a radius ofcurvature R_(C) in the respective plane of the bend. On the other hand,it may also be characterized by a length L of a curved segmentrepresenting such curved shape in a transversal cross-section in a planethat is perpendicular to light input edge 12.

Radius of curvature R_(C) may be constant across the area of light guide4 and may be measured at any point of surfaces 20 or 40. It may also bemade variable across the light guide's area and may be measured at therespective locations of surfaces 20 or 40. R_(C) is preferably greaterthan 5 times the thickness of the light guide, more preferably greaterthan 10 times, and even more preferably greater than 20 times thethickness of light guide 4 at each point of surfaces 20 and 40. On theother hand, at least a portion of light guide 4 has radius of curvatureR_(C) that is less than a certain maximum value. According to someembodiments, such maximum value may be defined by length L. According toone embodiment, radius R_(C) is less than 3 times length L. According toone embodiment, radius R_(C) is less than 2 times length L. According toone embodiment, radius R_(C) is less than 1.5 times length L. Accordingto one embodiment, radius R_(C) is less than 1.3 times length L.According to one embodiment, radius R_(C) is less than length L.

Reflector 30 is formed by an opaque sheet of a flexible and highlyreflective material. Reflector 30 is positioned adjacent to convexsurface 40 of light guide 4 so that its concave reflective surface isfacing the light guide and generally conforms to the curved shape of thelight guide. According to one embodiment, reflector 30 may be of aspecular type. For example, it may include a mirrored surface reflectinglight by means of specular reflection. According to one embodiment,reflector 30 may be of a diffuse type. For example, it may include adiffuse high-reflectance coating, such as white paint or white-powdercoating containing titanium dioxide. According to one embodiment,reflector 30 may be configured to reflect in both specular and diffuseregimes. For example, reflector 30 may have a mirrored surface whichincludes surface corrugations, waviness or microstructure that causesthe reflected rays to spread over a limited angular range. For instance,reflector 30 may be configured to reflect an incident parallel beam oflight into a cone of reflected light having a fixed angular spread(e.g., 10°, 20°, 30°, and so on).

The desired light-diffusing power of reflector 30 may also be definedbased on a Full Width Half Maximum (FWHM) angle characterizing suchdiffusely reflected beam. According to one embodiment, the surface ofreflector 30 is configured to reflect light at FWHM angle that is lessthan 60°. According to one embodiment, the FWHM angle is less than 30°.According to one embodiment, the FWHM angle is less than 20°. Accordingto one embodiment, the FWHM angle is less than 10°.

The desired reflective characteristics of reflector 30 may also bedefined based on proportions between secularly and diffusely reflectedlight. According to various embodiments, a ratio between the lightenergy reflected in a specular regime to the light energy reflected in adiffuse regime is any one of the following: 0.2, 0.4, 0.5, 0.6, 0.7, and0.8.

While surface 40 is ordinarily transparent, it may also be mirrored ormade diffusely reflective as an alternative to employing reflector 30.Reflective surface 40 may be formed by depositing a layer or reflectivematerial or film on top of it. The entire area of surface 40 or only itsselected areas may be made reflective. A reflective layer formed onsurface 40 may be provided with any of the properties described abovefor reflector 30.

Linear light source 10 is positioned in a close proximity to light inputedge 12 so that at least a 50% or more light emitted by the source canbe input into light guide 4 through such light input edge. Linear lightsource 10 may be exemplified by a fluorescent tube or a strip of LEDsextending parallel to light input edge 12. The LEDs may be incorporatedin a linear, two-dimensional array which may include one, three or morerows and a number of columns. The LEDs may also be distributed over thesurface of light input edge 12 according to a randomized two-dimensionalpattern.

Light extraction elements 6 may be formed, for example, by dots of whitepaint or ink printed on either one or both surfaces 20 and 40. Lightextraction elements 6 may also be formed by interruptions or protrusionsin otherwise smooth broad-area surfaces of light guide 4. Lightextraction elements 6 may be formed by light-deflecting surface relieffeatures including but not limited to grooves, cavities, microprisms,microlenses, holes, protrusions, or roughened portions of the lightguide surface. Such surface relief features may be formed in either oneor both of surfaces 20 and 40.

Light extraction elements 6 may also be formed by light deflectingparticles distributed throughout the volume of the body of light guide4. By way of example, such light deflecting particles may includesub-micron size light-scattering particles embedded into the material oflight guide 4. In a further example, such light deflecting particles maybe formed by macroscopic inclusions of a dielectric material having adifferent refractive index than the material of light guide 4.

According to further embodiments, light extraction elements 6 may beformed by forward-scattering particles or relatively shallow surfacerelief structures configured to incrementally deflect light rays fromthe original propagation path by relatively small angles upon eachinteraction. Examples particularly include shallow surface corrugationsand volumetrically distributed forward-scattering particles. Such lightdeflecting structures and elements are disclosed in U.S. PatentApplications Publication No. 2014/0140091, the disclosure of which isincorporated herein by reference in its entirety.

In the context of at least a preferred embodiment of the presentinvention, the term “forward scattering” is directed to mean thescattering of light involving a change of direction of less than 90degrees. When applied to the propagation of a light ray through aforward-scattering medium, the light ray can be considered forwardscattered when it is randomly deflected by the medium from the originalpropagation path towards a direction that makes an angle with theoriginal propagation direction of less than 90 degrees. Similarly, theterm “forward deflection” with respect to a light ray is directed tomean the deflection of such light ray at an angle of less than 90degrees with respect to the original propagation path.

It is noted that, according to at least some embodiments, theforward-scattering operation of forward-scattering medium does notpreclude backscattering (scattering in a generally backward direction)in which a portion of the incident light is scattered at angles of 90degrees or more with respect to the incidence direction. Furthermore,according to at least some embodiments, it may be desired thatbackscattering accompanies the forward scattering. The proportionsbetween the forward scattered and backscattered light energy may vary ina broad range. According to one embodiment, more than 50% of theincident light can be forward scattered and less than 50% of theincident light can be backscattered. According to one embodiment, morethan 50% of the incident light can be backscattered and less than 50% ofthe incident light can be forward scattered. According to oneembodiment, no less than 20% of the incident light energy is forwardscattered and no less than 20% of the incident light energy isbackscattered. According to one embodiment, no less than 30% of theincident light energy is forward scattered and no less than 30% of theincident light energy is backscattered. According to one embodiment, noless than 40% of the incident light energy is forward scattered and noless than 40% of the incident light energy is backscattered. Accordingto one embodiment, the proportions between the forward scattered andbackscattered portions of the light energy (after the subtraction of theabsorbed light, if any) can be either one of 60%/40%, 70%/30%, 80%/20%,20%/80%, 30%/70%, and 40%/60%. Furthermore, according to at least oneembodiment, the forward-scattering angle can be much less than 90degrees, for example, 60 degrees, 45 degrees, or 30 degrees. Accordingto one embodiment, the forward-scattering angle is one of the followingranges: less than 60 degrees, less than 45 degrees and less than 30degrees.

FIG. 2 schematically illustrates shaped illumination device 900 in across-section that is perpendicular to light input edge and parallel toa plane of a prevailing curvature of the device. Illumination device 900of FIG. 2 has the shape of an arc of a circle in such cross-section. Ithas a constant radius of curvature R_(C) being less than 1.2 times awidth of the sheet that forms light guide 4 (as measured in theillustrated cross-section).

Linear light source 10 is exemplified by an LED 2 enclosed into anextruded structural channel 50. It should be understood that lightsource 10 may include any suitable number of LEDs 2 distributed alongthe length of light input edge 12 (and channel 50) according to anysuitable pattern. Each LED 2 may be of an inorganic type and may includeone or more LED chips or dies incorporated into an LED package. Such LEDchips or dies may be arranged in one-dimensional or two-dimensionalarray within the LED package and may be encapsulated by a layer ofoptically transmissive encapsulation material. The encapsulationmaterial may include phosphors for wavelength conversion of lightemitted by the LED chips or dies.

The light input portion of light guide 4 that encompasses light inputedge 12 and adjacent areas of surfaces 20 and 40 may further includelight-coupling optics that enhances light injection into light inputedge 12. Yet further, a layer of a transparent, index-matched dielectricmaterial (such as silicone or UV-curable acrylic, for example) may beprovided between LED 2 and light input edge 12 to fill the air gap andenhance light coupling from the LED to the light guide. Various examplesof LEDs and light coupling optical elements suitable for enhanced lightinput into sheet-form light guides are disclosed in a co-pending U.S.Patent Applications Publication No. 20170045666, the disclosure of whichis incorporated herein by reference in its entirety, and U.S. PatentApplications Publication No. 20140226361, the disclosure of which isincorporated herein by reference in its entirety. When such lightcoupling optics is used, a light emitting aperture of LED 2 may have asize that is greater than a thickness of sheet-form light guide 4 atlight input edge 12. Otherwise, it is preferred that the light emittingaperture of LED 2 is approximately equal to or less than the light guidethickness at light input edge 12.

Light input edge 12 may be specially shaped to facilitate light couplinginto light guide 4. Edge 12 may include cavities, protrusions,extensions and thicker or thinner areas or portions. Light input edge 12may also include a tapered portion. Opposing edge 14 may also beconfigured for light input and shaped or configured according to thesame principles described above for light input edge 12.

Light may also be input into light guide 4 through either one or bothbroad-area surfaces 20 and 40. Examples of such light input throughbroad-area surfaces (faces) of planar waveguides are disclosed in detailin U.S. Patent Applications Publications Nos. 20170045666 and20140226361. In various implementations of shaped illumination device900, LEDs 2 may also be embedded into the body of light guide 4.

Channel 50 is configured to provide structural support for light source10 and may at least partially enclose the light source. Referring to theembodiment of FIG. 2, extruded channel 50 may be designed to hold LED 2in a prescribed place and orientation with respect to light input edge12. It is preferred that channel 50 is made from a material that hashigh thermal conductivity and structural strength. Conventionally,channel 50 can be made from aluminum extrusion and configured to provideenhanced heat dissipation from LED 2. Channel 50 may optionally includeheat dissipating fins (not shown) extending parallel or perpendicular toa longitudinal axis of the channel and configured to remove heat fromLED 2. Each LED 2 may be attached/bonded to channel 50 with a goodmechanical and thermal contact.

According to one embodiment, at least some light extraction elements 6are configured to extract light from light guide 4 and cause lightemission from at least concave broad-area light input/output surface 20.Furthermore, it is preferred that at least a substantial portion oflight exits from surface 20 at relatively high emergence and is directedgenerally towards edge 14 of light guide 4. According to one embodiment,at least some light extraction elements 6 are configured to extractlight from light guide 4 and cause light emission from at least convexbroad-area light input/output surface 40. According to one embodiment,at least one of light extraction elements 6 is configured to extractlight from light guide 4 through both surfaces 20 and 40.

A cone of light 290 schematically illustrates a directional light beamemitted from a particular area of surface 20. Such light beam may have asharply asymmetric angular distribution such that most of the extractedlight rays form a relatively low angle with respect to their originalpropagation direction in light guide 4 and a relatively high angle withrespect to a surface normal. For example, at a given light emittinglocation of surface 20, an angle between a prevailing direction of lightpropagation and a normal to surface 20 may be greater than 30°, greaterthan 45°, greater than 60°, and greater than 70°. The prevailingpropagation direction of the emergent light beam should also generallybe pointing away from light input edge 12. The emission angles and thesize and curvature of light guide 4 are preferably selected such that atleast one different area of concave surface 20 is positioned in energyreceiving relationship with respect to the extracted/emitted light andis configured to intercept at least a portion of such extracted/emittedlight. For example, as illustrated in FIG. 2, an area of surface 20adjacent to edge 14 may be positioned in energy receiving relationshipwith respect to a light emitting area of surface 20 that is located in aproximity to light input edge 12.

It is noted that cone of light 290 is shown for illustrative purposesonly. It is also shown to indicate a sharply asymmetric angulardistribution of the beam emitted from concave surface 20. However, it isfurther noted that the operation of shaped illumination device 900 doesnot preclude emitting light from surface 20 at angles outside of suchcone of light 290. It should be understood that portions of light energymay be emitted from surface 20 at any angle within the full ±90° angularrange (with respect to a normal to surface 20 at the correspondingemission point). More particularly, a significant fraction of light canbe emitted toward a normal direction with respect to surface 20.According to one embodiment, a substantial fraction of light may also beemitted generally towards a source direction.

A luminance of surface 20 at any given location and at a particularemission angle may be measured using a luminance meter, such as, forexample, LS-100/110 or LS-150/160 spot luminance meters commerciallyavailable from Konica Minolta, Inc. The angular asymmetry of the lightbeam emitted from a particular area of light-emitting surface 20 may beassessed by measuring surface luminance at different angles with respectto a surface normal. The angular luminance distribution of the entirelight-emitting surface 20 may be measured using a goniophotometer suchas those used for evaluating lighting fixtures.

Let's define an on-axis luminance E_(on-axis) of light-emitting surface20 at a given point of the surface as a luminance measured within anangular range from 0° and 45° with respect to a surface normal at suchpoint. Let's further define an off-axis luminance E_(off-axis) oflight-emitting surface 20 at the same point as a luminance measuredwithin an angular range between 45° and 90° with respect to the surfacenormal. According to different embodiments, it is preferred that amaximum off-axis luminance E_(off-axis) at a mid-point of surface 20 isgreater than a maximum on-axis luminance E_(on-axis) at least by afactor of 1.2, 1.3, 1.4, and 1.5. It may further be preferred thatoff-axis luminance E_(off-axis) measured from a direction 82 (e.g.,using a luminance meter 86 which light receiving aperture 88 isgenerally facing light input edge 12) is substantially greater (e.g., bya factor of 1.5, 2, 3, or more) than off-axis luminance E_(off-axis)measured from a direction 84 (e.g., with light receiving aperture 88 ofluminance meter 86 generally facing away from light input edge 12).

It may be appreciated that the embodiments of shaped illumination device900 employing reflector 30 of a diffuse type may exhibit a reducedasymmetry of the emitted light beam compared to the cases wherereflector 30 is of a specular type or where the device is used withoutany reflector. This is primarily due to the fact that diffuse reflector30 introduces random light propagation directions to the total lightbeam emitted by the device and may therefore partially or completelymask the asymmetric angular distribution produced by light guide 4alone. Yet, it is noted that, according to at least some embodiments,Illumination device 900 may be configured to emit light with ameasurable asymmetrical angular distribution of the emitted beam even inthe presence of diffuse reflector 30.

Different modes of operation of shaped illumination device 900 arefurther illustrated by example of light rays 22, 24, and 26 emanated byLED 2 and schematically depicted by solid, dashed and dotted lines,respectively.

Ray 22 (solid line) enters light guide 4 via light input edge 12 andpropagates in the body of the light guide towards opposing edge 14 inresponse to optical transmission and TIR until it encounters one of theplurality of light extraction elements 6. The respective lightextraction element 6 deflects ray 22 away from a surface plane and outof light guide 4. According to one embodiment, it is preferred thatlight extraction element 6 deflects ray 22 by means of a forwarddeflection or forward scattering. As a result, ray 22 exits from lightguide 4 through concave light-output surface 20. The emergence angle issuch that ray 22 propagates generally away from light input edge 12 andtowards opposing edge 14, forming a relatively low propagation angle(significantly less than 90°) with respect to surface 20.

Ray 24 (dashed line) is likewise emitted by LED 2 and coupled to lightguide 4 through its light input edge 12. Ray 24 initially propagates ina waveguide mode until it strikes one of the forward-deflecting orforward-scattering light extraction elements 6 relatively near lightinput edge 12. Ray 24 is deflected away from its original propagationpath and emitted from surface 20 at a location 52. Upon the exit fromlight guide 4, ray 24 forms a relatively high emergence angle θ_(E) withrespect to a surface normal 44 and further travels through air alongsurface 20 and towards opposing edge 14 of waveguide 4. The area ofillumination device 900 near edge 14 is curved appropriately andconfigured to intercept such light rays propagating at near-grazingangles with respect to surface 20. As a result, ray 24 that travels aconsiderable distance outside of light guide 4 enters the light guidefor the second time at a location 54. Upon the re-entry, ray 24propagates transversely through light guide 4, undergoing doublerefraction at surfaces 20 and 40, exits from surface 40 and strikesreflector 30 beneath light guide 4. Reflector 30 reflects ray 24 withsome forward scattering and causes at least a substantial portion oflight energy of ray 24 to be emitted from surface 20 in the form of adivergent light beam, as schematically illustrated in FIG. 2. Suchdivergent light beam further propagates away from surface 20 andcontributes to the total light beam produced by illumination device 900.

Accordingly, ray 24 initially emerging from light guide 4 relativelyclose to light input edge 12 (at location 52) and at a relatively highemergence angle θ_(E) is trapped by illumination device 900, recycledand re-emitted from a different area of the light guide (at location54). The final propagation direction of ray 24 may be different from itsinitial propagation direction. Such difference may constitute, forexample 45°, 60°, or 90°. The final propagation directions and theemission cone may be controlled by the slope of reflector 30 and itsreflective properties (e.g., a diffusion angle). It may be appreciatedthat such controlled recycling of light rays may be advantageously usedto spatially and angularly redistribute the light beam and providevarious prescribed emission patterns. For instance, shaped illuminationdevice 900 may be configured to emit a relatively narrow (collimated)light beam with relatively uniform light intensity.

According to an aspect, illumination device distributes light emitted byLED 2 by means of light propagation though light guide 4 and also bymeans of propagation of a portion of light outside light guide 4 throughthe volume formed by the curved shape of flexible sheet that forms thelight guide.

According to different embodiments, shaped illumination device 900 isconfigured for asymmetric light outcoupling from light guide 4 such thatat least a substantial portion of light emerging from the light guidehas exit angles (emergence angles) below 40°, below 30°, below 20°, orbelow 10°. Furthermore, reintroducing light initially emitted at a firstlocation of light guide 4 (e.g., near light input edge 12) at adifferent second location (e.g., near opposing edge 14), as illustratedby ray 24, may be advantageously used to increase the luminance ofdevice 900 at the second location. For example, portions of shapedillumination device 900 near edge 14 may otherwise receive insufficientamount of light due to the depletion of light energy in light guide 4 asthe light travels from light input edge 12 to the opposing edge 14. Thismay particularly be the case in embodiments of shaped illuminationdevice 900 in which light extraction elements 6 are identical and alsospaced identically across the area of light guide 4. In suchembodiments, light extraction elements 6 may progressively extract fewerand fewer light from light guide 4 as the distance for light input edge12 increases. Without light recycling, a light emitting area of shapedillumination device 900 near opposing edge 14 may appear considerablydarker than a similar area near light input edge 12 or at a mid-sectionof the device. Thus, recapturing and re-emitting some of thehigh-emergence-angle by the areas of device 900 near edge 14 may atleast partially compensate such light depletion and enhance thebrightness uniformity across the light emitting surface of the device.

Ray 26 (dotted line) initially propagates within light guide 4 in awaveguide mode in response to optical transmission and bouncing fromsurfaces 20 and 40 by means of TIR until it strikes one of lightextraction elements 6. Unlike rays 22 and 24, ray 26 is deflectedtowards convex surface 40 of light guide 4, as a result offorward-deflecting or forward-scattering operation of the respectivelight extraction element 6. Accordingly, ray 26 emerges from light guide4 towards reflector 30. Reflector 30 reflects ray 26 with somescattering and causes at least a substantial portion of the light energyof ray 26 to be emitted from surface 20 away from illumination device900 in the form of a diffuse light beam. The diffusion angle may becontrolled by the reflective properties of the surface of reflector 30and/or the forward-scattering properties of light deflecting element 6.According to one embodiment, shaped illumination device 900 isconfigured to emit light from the entire exposed surface 20 intoprescribed directions such that the apparent brightness of the surfaceis relatively uniform when viewed from at least one of those directions.

Since surfaces 20 and 40 are curved, light propagating in light guide 4may receive additional angular bias compared to the case of a planarlight guide having the same dimensions and structure. It may beappreciated that at least some of the outermost out-of-plane light raysinitially propagating in light guide by TIR may eventually escape fromcurved light guide 4 even without encountering light extraction elements6. It may further be appreciated that such escaping light rays mayemerge at near-grazing angles with respect to the light emittingsurface. Since both surfaces 20 and 40 are transparent and permeable tolight propagating at below-TIR angles, light may escape at near-grazingangles from either one or both sides of light guide 4. According to oneembodiment, the curvature of light guide 4 may be selected so that theemergence angles of the escaping light rays are generally above 60° withrespect to a surface normal (or below 30° with respect to thelight-emitting surface) at the respective escape location. According toone embodiment, the curvature of light guide 4 may be selected so thatlight primarily emerges at angles generally above 70° with respect to asurface normal (or below 20° with respect to the light-emittingsurface). Light rays emerging form light guide 4 at such angles may berecycled, angularly redistributed and re-emitted from shapedillumination device 900 at according to the mechanisms described aboveby example of rays 22, 24 and 26.

According to one embodiment, shaped illumination device 900 may beimplemented without curved reflector 30 in which case light exiting fromsurface 40 will leave the device and can be used for two-sides emission(e.g., light can be emitted from both opposing surfaces 20 and 40).According to one embodiment, reflector 30 may be provided on the side ofconcave broad-area surface 20 in which case nearly all of the lightemitted by device 900 can be emanated from convex broad-area surface 40.According to some embodiments, shaped illumination device 900 may beimplemented without light extraction elements 6 and the light trapped inlight guide 4 may be extracted by other means, for example, byappropriately curving and/or tapering the light guide along its lengthfrom light input edge 12 to opposing edge 14.

It may be appreciated that edge-lit systems typically require a variabledensity or variable sizing of light extraction features to provide arelatively uniform light output from the light-emitting surface of alight guide. At one-sided light input, the density or sizes of lightextracting features typically increase from a light input edge towardsthe opposing edge. In contrast, light recycling described above allowsmore light to be emitted from a portion of light guide 4 opposing tolight input edge 12 than it would have otherwise been possible with aplanar light guide of the same dimensions and internal structure. Inview of this, according to one embodiment, shaped illumination device900 may include light extraction elements 6 that are identical and havea generally uniform distribution density over the light emitting area oflight guide 4 (e.g., constant spacing and sizes). By using the lightrecycling principles described above, such illumination device may beconfigured to provide a relatively uniform apparent brightness of itslight-emitting surface at least at some viewing angles. According to analternative embodiment, shaped illumination device 900 may include lightextraction elements 6 distributed over the area of light guide 4according to a varying pattern but such pattern may be different fromthe one which would be required for a planar configuration of lightguide 4 to provide the same level of luminance uniformity. For example,the density of light extraction elements 6 may increase from light inputedge 12 to opposing edge 14. In a further example, the size or lightextraction elements 6 may increase from light input edge 12 to opposingedge 14 while the density may be kept constant.

According to one embodiment, at least some of the light propagated inlight guide 4 may also be emitted from edge 14 towards directions thatare different from the original propagation direction of light emittedby LED 2. An angle between the original propagation direction and theprevailing direction of light emergence from edge 14 may beapproximately equal to an effective bend angle of light guide 4.

FIG. 3 schematically shows, in a transversal cross-section that isperpendicular to surfaces 20 and 40 and light input edge 12, anembodiment of shaped illumination device 900 which is identical to thatof FIG. 2 except that light extraction elements 6 are also formed insurface 20. A reference line 200 is parallel to an optical axis of LED 2and perpendicular to light input edge 12. The optical axis of LED 2 maybe defined as an axis that crosses the center of a light emittingaperture of LED 2 and is perpendicular to such light emitting aperture.Alternatively, the optical axis may also be defined as an axis thatcrosses the center of a light emitting aperture of LED 2 and is parallelto a direction of the maximum intensity of light emitted by LED 2. Inthe illustrated case, reference line 200 is perpendicular to the planarsurface of light input edge 12 and parallel to portions of surfaces 20and 40 adjacent to light input edge 12. Reference line 200 alsoindicates a tangent plane to surface 20 near light input edge 12.Referring further to FIG. 3, a reference line 202 indicates a tangentplane to surface 20 at opposing edge 14.

Let's define a bend angle β of shaped illumination device 900 as anangle between the tangent planes at light input edge 12 and opposingedge 14. According to one embodiment, bend angle β is equal to orgreater than 20°. According to one embodiment, bend angle β is greaterthan 20° and less than 90°. According to one embodiment, bend angle β isgreater than 30° and less than 90°. According to one embodiment, bendangle β is greater than 45° and less than 90°. According to oneembodiment, bend angle β is about 90°. According to one embodiment, bendangle β is greater than 90° and less than 180°.

In view of the discussion presented in reference to FIG. 2, it may beappreciated that a beam of light emitted by shaped illumination device900 may be advantageously limited to generally exclude light propagationalong directions that make relatively small angles with respect toreference line 200. A critical cutoff angle α of light emission may bedefined as an angle between reference line 200 and a reference line 204that connects opposing edges 12 and 14 of light guide 4. According toone embodiment, less than 10% of the total light energy emitted byshaped illumination device 900 propagates at angles below angular cutoffangle α. According to one embodiment, less than 5% of the total lightenergy emitted by shaped illumination device 900 propagates at anglesbelow angular cutoff angle α. Shaped illumination device 900 may also beconfigured such that virtually no light is emitted below such angularcutoff. Accordingly, substantially all of the light emission may bedirected to a relatively narrow, prescribed angular range. Sucharrangements may basically preclude a direct view of the light inputedge at viewing angles below cutoff angle α. They may also beadvantageously employed for designing lighting luminaires that emit atleast partially collimated light and provide masking of the light source(such as high-brightness LEDs) to prevent or minimize glare that may becaused by such light source. According to different embodiments, shapedillumination device 900 is configured to provide cutoff angle α of atleast 10°, at least 20°, at least 30°, at least 40°, and at least 45°.According to different embodiments, the total emission angle of shapedillumination device 900 may be less than 140°, less than 120°, less than90°, less than 60° and less than 45°. A FWHM emission angle of shapedillumination device 900 may be less than 100°, less than 90°, less than45°, and less than 35°.

While LED 2 is shown being coupled to light input edge 12 by positioninga light emitting aperture of the LED in a close proximity to the lightinput edge, other forms of LED 2 coupling to light guide 4 may be used.For example, light can be coupled to light guide 4 partially or entirelythrough one or both of its surfaces 20 and 40, or through a combinationof light input edge 12 and surfaces 20 and/or 40. Furthermore, accordingto one embodiment, a refractive index matching layer of an opticallytransmissive material may be provided between LED 2 and light input edge12 of light guide 4 to eliminate the respective air gap and suppressFresnel reflections within the material of LED 2. Examples of suchdifferent forms of light coupling into light guide 4 may be found, forexample, in U.S. Patent Application Publications Ser. No. 20170045666and 20140226361, the disclosures of which are incorporated herein byreference by their entirety.

FIG. 4 schematically depicts an embodiment of shaped illumination device900 in which curved light guide 4 has a tapered configuration. Suchlight guide 4 has a larger thickness at light input edge 12 and asubstantially smaller thickness at opposing edge 14. Broad-area surfaces20 and 40 gradually converge towards each other at edge 14 so that thebody of light guide 4 has the form of a thin, curved wedge.

In operation, a light ray 112 coupled to light guide 4 through its widerlight input edge 12 is propagated towards opposing narrower edge 14undergoing multiple TIRs from surfaces 20 and 40. Since surfaces 20 and40 are not exactly parallel to each other and are further curved, apropagation angle of ray 112 with respect to such surfaces progressivelyincreases with each bounce until it becomes less than a critical angleof TIR characterizing the material of light guide 4.

At this point, ray 112 exits from light guide 4, undergoing refractionat surface 20, and further propagates along surface 20 at near-grazingangle. Subsequently, ray 112 strikes a curved portion of light guide 4at another location (e.g., near opposing edge 14) where at least asubstantial portion of its energy is reflected by means of a Fresnelreflection, contributing to the total collimated light beam emitted bydevice 900.

It is noted that such secondary Fresnel reflection from surface 20 isillustrated by way of non-limiting example only and as one of thepossible scenarios of light propagation. For example, depending on theemergence angle and the geometry of shaped illumination device 900, ray112 may also undergo refraction at the secondary interaction withsurface 20 and can be recycled and re-emitted, similarly to ray 24 ofFIG. 2. Furthermore, when an emergence angle of ray 112 is sufficientlylow (with respect to a surface normal), it may completely avoid thesecondary interaction with surface 20 and may thus continue itspropagation along the original emission direction. Considering variouspossible scenarios of light propagation, it may be appreciated that thelight guide 4 having a tapered configuration may be configured to emit ahighly asymmetric light beam with relatively high emergence angles, asillustrated by cone of light 290.

While the embodiment of shaped illumination device 900 may be configuredto redistribute and emit light from its entire surface even withoutlight extraction elements 6, such light extraction elements may still beprovided to enhance the light extraction rate and/or enhance theuniformity of light emission. In other words, the wedge-shapedconfiguration of light guide 4, its curved shape and the plurality oflight extraction elements 6 may act cooperatively to extract light fromlight guide 4 and contribute to the total emission flux of device 900.

FIG. 5 schematically illustrates an embodiment of illumination device900 in which light extraction elements 6 are exemplified byforward-scattering surface relief features that are formed in bothsurfaces 20 and 40 and represent discrete bulges of light scatteringmaterial protruding from the respective surfaces. According to oneembodiment, each of these bulges may have a rounded hemispherical shapein a cross-section.

Several examples of different shapes of the bulges are illustrated inFIG. 6 through FIG. 10. The top surface of the bulge may be curved sothat the bulge has a variable thickness gradually decreasing from itscenter to the periphery (FIG. 6 and FIG. 7). According to oneembodiment, each of the bulges may have a rounded “hat”-type shape in across-section (FIG. 8). According to one embodiment, each of the bulgesmay have a relatively low thickness and flat or nearly flat top surfacethat extends about parallel to the respective surface (FIG. 9).According to one embodiment, the top surface of each bulge may beirregular (FIG. 10) or microstructured and the respective irregularitiesor microstructures may be configured to enhance scattering of theextracted light.

According to one embodiment, an average thickness of each bulge isbetween 2 micrometers and 15 micrometers. For example, an individualbulge may have a thickness of 6 micrometers, 8 micrometers, 10micrometers or 15 micrometers at a highest point and a reduced thicknessof only 2, 3, 4 or 5 micrometers at peripheral areas. The outermostperipheral areas of the bulges may have thicknesses that are below 1micrometer (e.g., 0.1 or 0.5 micrometers).

According to one embodiment, the thickness of the light-extractingsurface relief features and the load of forward-scattering particles areselected such that each light extraction element 6 is semi-opaque.According to one embodiment, each light extraction element 6 isconfigured to partially transmit light, with some forward scattering,and partially reflect light back toward the source, with somebackscattering, when illuminated.

The forward-scattering and backscattering properties of the materialforming semi-opaque, back-scattering light extraction element 6 may beevaluated, for example, by measuring a bidirectional scatteringdistribution function (BSDF) for a uniform layer of the same materialdeposited to a surface of a glass or acrylic plate. Such plate or filmshould preferably be made from the same or similar material as lightguide 4 and may also have a similar thickness. The coating shouldpreferably have a uniform thickness approximating the average thicknessof the bulges forming forward-scattering light extraction elements 6.For such measurements, the coated plate or film can be illuminated by acollimated light source from a perpendicular direction. As a practicalconsideration, the BSDF function may also be customarily obtained byseparately measuring BRDF (bidirectional reflectance distributionfunction) and BTDF (bidirectional transmittance distribution function).A ratio between the forward-scattered and backscattered light can beestimated by dividing the total transmitted light energy by the totalreflected light energy. In a variation of the technique, themeasurements may be adapted to employ illuminating the sample from adirection that makes an angle of about 45 degrees with respect to asurface normal.

According to one embodiment, the material of semi-opaque,forward-scattering light extraction elements 6 may be selected such thatan energy ratio between the forward-scattered (diffusely transmitted)light and the backscattered (diffusely reflected) light measuredaccording to the above-described technique falls into one of thefollowing ranges: 0.2 to 0.3, 0.3 to 0.4, 0.4 to 0.5, 0.5 to 0.6, 0.6 to0.7, and 0.7 to 0.8. According to one embodiment, no less than 20% ofthe incident light energy is forward scattered and no less than 20% ofthe incident light energy is backscattered. According to one embodiment,no less than 30% of the incident light energy is forward scattered andno less than 30% of the incident light energy is backscattered.According to one embodiment, no less than 40% of the incident lightenergy is forward scattered and no less than 40% of the incident lightenergy is backscattered. The specific ratios between theforward-scattered and backscattered light exemplified above can beachieved, for example, by properly selecting the sizes and volumetricload of the light scattering particles in a clear binder or resin thatis used to produce the forward-scattering material of light extractionelements 6.

According to one embodiment, the volume of each bulge may be between10000 cubic micrometers and 100000 cubic micrometers. According to oneembodiment, the volume of each bulge may be between 10000 cubicmicrometers and 500000 cubic micrometers. According to one embodiment,the sizes and volumes of the bulges may vary across surfaces 20 and/or40 from 1000 cubic micrometers to 500000 cubic micrometers. For example,some individual bulges may have volumes of around 10000 cubicmicrometers or less and some individual bulges may have volumes ofaround 30000 cubic micrometers, 40000 cubic micrometers, 60000 cubicmicrometers, 100000 cubic micrometers or more.

According to one embodiment, the size (e.g., a diameter of the contactarea of the bulge with surface 20 or 40) of individual bulges can bewithin one of the following ranges: 20 to 200 micrometers, 10 to 20micrometers, 20 to 60 micrometers, 60 to 100 micrometers, 100 to 200micrometers, and 200 to 500 micrometers. The sizes may also vary fromone bulge to another. For example, a first group of bulges may havesizes between 10 and 50 micrometers and a second group of bulges mayhave sizes between 100 and 150 micrometers. The bulges of differentsizes, volumes, thicknesses and shapes may be mixed to cover anindividual area of light guide 4, according to a randomized pattern,where bulges of one size can be alternated with bulges of another sizeor sizes. The shapes may be regular (e.g., round, elliptical,square/rectangular, rectangular with rounded corners) or irregular(e.g., dumb-bell shaped, comma-shapes, having complex geometries ormultiple curvatures of the respective outline).

Forward-scattering light extraction elements 6 that are formed in or onsurface 20 may be distributed over the area of light guide 4 accordingto a first two-dimensional pattern and forward-scattering lightextraction elements 6 that are formed in surface 40 may be distributedover the area of light guide 4 according to a second two-dimensionalpattern which may be the same or different from the first pattern.Either one or both patterns may be ordered or random and may haveconstant or variable distribution densities over the respectivesurfaces. For example, the density may increase with the distance fromLED 2.

Each of forward-scattering surface relief features that form lightextraction elements 6 is disposed with a good optical contact with thesurfaces on which it is formed and includes forward-scattering particles9 distributed throughout its volume. According to one embodiment, theforward-scattering particles include non-light-absorbing white pigmentwhich may include, for example, nanoparticles of titanium dioxide havingsizes from 200 to 400 nanometers and configured to deflect light bymeans of a diffraction and optionally by a refraction. According to anaspect, forward-scattering light extraction elements 6 formed in surface40 and the light-scattering particles 9 that they contain represent anarea-distributed forward-scattering layer disposed between surface 40and reflector 30 and optically coupled to light guide 4.

The respective surface relief features may be formed by depositing smalldrops of white ink or paint on surface 40 in a liquid form with thesubsequent curing, e.g., by UV light. Such ink or paint may include auniform suspension of forward-scattering particles 9 in a clear resin orbinder. Individual drops of the white ink or paint may be deposited tosurface 40 by means of piezo-actuated ink jet printing and cured by a UVLED lamp, for example. A hollow spacing layer 31 between surface 40 andreflector 30 should be sufficient to accommodate the height ofsurface-protruding light extraction elements 6.

In operation, referring to FIG. 5, a light ray 121 emanated by LEDsource 12 (not shown) and propagating in light guide 4 in response toTIR and optical transmission strikes one of forward-scattering lightextraction elements 6 where it is split into two or more rays. A portionof ray 121 is deflected by forward-scattering particles 9 towardsreflector 30, as indicated by a light ray 122. Ray 122 is subsequentlyreflected from reflector 30 and exits from light guide 4 through surface20.

A light ray 123 illustrates a portion of light ray 121 that is reflectedby the material of light extraction element 6 directly toward surface20, similarly with some forward scattering. Both rays 122 and 123 areemitted at relatively high angles with respect to normal 44.Accordingly, considering multiple light rays propagating in light guide4 at different angles with respect to surfaces 20 and 40, eachrelatively small portion of surface 20 may be configured to emit lightin a forward direction (away from LED 2) and within a narrow angularrange, as illustrated by cone of light 290.

A light ray 126 illustrates light that is extracted from light guide 4by individual light extraction element 6 that is formed on surface 20.Ray 126 enters the respective surface relief feature (e.g., a bulgeformed by a cured drop of a light scattering while-pigmented ink) and isforward scattered away from the extraction location and out of lightguide 4. Similarly, multiple rays propagating in light guide 4 andstriking the respective light extraction element 6 can be forwardscattered, forming a cone of light 291.

FIG. 11 schematically illustrates light extraction elements 6exemplified by shallow (having low-angle reflective/refractive facets)prismatic surface relief features that provide forward-deflectingfunction with respect to light rays propagating in light guide 4. Morespecifically, the prismatic surface relief features are represented bymicro-prismatic grooves formed in surfaces 20 and 40. Themicro-prismatic grooves have a triangular cross-section and slopedsurfaces configured to extract light from light guide 4 using refractionand/or TIR and to provide relatively high emergence angles of lightrays, as illustrated by emission cone 290. FIG. 12 illustrates adifferent mode of light extraction using such prismatic surface relieffeatures and reflector 30, also resulting in a low-angle off-axisemission.

FIG. 13 schematically illustrates an embodiment of shaped illuminationdevice 900 having enhanced optical coupling between LED 2 and lightguide 4. It also schematically illustrates a yet further mode of lightextraction from light guide 4 at high emergence angles. A layer 32 ofindex-matched optical material is provided between LED 2 and light inputedge 12 such that the material completely fills the air gap between thelight emitting surface of LED 2 and the light-receiving surface of lightinput edge 12. The material of layer 32 should have a refractive indexsubstantially greater than that of air (n_(air)≈1). A preferable rangeof the refractive index is 1.4-1.8. According to one embodiment, layer32 may have a refractive index approximating that of light guide 4.According to one embodiment, layer 32 may have a refractive indexapproximating that of an encapsulation layer that may be employed in LED2.

In operation, light rays emitted by LED 2 at low off-axis angles aretrapped within light guide 4 and propagate in a waveguide mode. Lightrays emitted by LED 2 at relatively high off-axis angles may exit fromsurface 20 in a vicinity of light input edge 12 and form relatively highemergence angles. Accordingly, some of the emergent rays, at least thosehaving the highest emergence angles (with respect to a surface normal),may be intercepted by other portions of shaped illumination device 900and recycled and re-emitted from such other portions at differentemergence angles, according to the principles discussed above.

It may be appreciated that the refractive index matching may be also beadvantageously used to enhance the efficiency of light extraction fromLED 2 by providing a gapless light transfer from the respective LEDchips to light guide 4 for light rays that could otherwise be trappedand lost within the LED package. Thus, the illustrated configuration ofshaped illumination device 900 may allow emitting more light from therespective LEDs compared to the bare LED packages that are not coupledto light guide 4 using the refractive index matching.

FIG. 14 depicts a schematic exemplary dependence of surface luminance oflight guide 4 from the emission angle in a plane parallel to aprevailing direction of light propagation in light guide 4. The emissionangle is measured with respect to a surface normal. The negativeemission angles correspond to angles measured from a surface normaltowards light input edge 12 and the positive emission angles correspondto angles measured from a surface normal towards opposing edge 14. Sinceeach of surfaces 20 and 40 of light guide 4 may be configured to emitlight, each of such surfaces may be characterized by its own angulardependence of surface luminance which may resemble that of FIG. 14.

When measuring a localized surface luminance representing a particulararea of light guide 4 or shaped illumination device 900, it is preferredthat the shape and size of a sampling area approximates the shape andsize of the area to be evaluated. For a spot measurement of the surfaceluminance, the sampling area should preferably be much smaller than thetotal area of the light emitting surface. Spot measurements may also beconventionally done employing a round or quasi-round sampling area. Forexample, for spot measuring of the surface luminance of surface 20 thathas a characteristic dimension of 20 cm or more, the size of thesampling area may be from several millimeters to a couple ofcentimeters.

The angular dependence of surface luminance may be characterized by apeak luminance L_(p) and an angle α_(p) corresponding to such peakluminance. According to different embodiments, the angular distributionof a spot surface luminance of light guide 4 and/or the respectivelight-emitting surface of shaped illumination device 900 may be boundedby specific relationships between peak emission angle α_(p) and bendangle β, e.g., in order to achieve optimal regimes of recycling lightemitted from light guide 4 through secondary interactions of the emittedlight with the light guide according to the principles discussed above.Such spot peak emission may be measured at an area of surface 20relatively near light input edge 12 or at a mid-point of surface 20, forexample.

According to one embodiment, 90°−α_(p)<1.5β. According to oneembodiment, 90°−α_(p)<2β. According to one embodiment, 90°−α_(p)<β.According to one embodiment, 1.5(90°−α_(p))<β. According to oneembodiment, 2(90°−α_(p))<β. In other words, the shape and curvature oflight guide 4 may be selected such that at least a substantial part oflight emitted in a vicinity of light input edge 12 or at a mid-point ofthe light emitting surface could be intercepted and recycled by an edgeportion of shaped illumination device 900.

One portion of shaped illumination device 900 (e.g., one half of thelight emitting area of light guide 4 adjacent to edge 14) may beconfigured to intercept and recycle a certain percentage of light energyemitted from another portion of the shaped illumination device 900(e.g., the other half of the light emitting area of light guide 4 thatis adjacent to edge 12). According to different embodiments, suchpercentage may be 20%, 30%, 50%, 60% and 75%.

The location of the light beam recapture and recycling may be at aconsiderable distance from the location of the initial emission. Forexample, light may initially be emitted from a vicinity of light inputedge 12 or a mid-point of surface 20 and then intercepted and recycledin a vicinity of opposing edge 14. According to one embodiment, thedistance between the location of initial emission and the location oflight re-entry into light guide 4 is substantially greater than athickness of light guide 4. For example, such distance may be at least 2times, 5 times, 10 times, 20 times, and 50 times greater than the lightguide thickness. According to some embodiments, the distance between thelocation of initial emission and the location of light re-entry intolight guide 4 is greater than 10%, 20%, 30%, 40%, or 50% of the size ofthe light emitting area of surface 20 or a width of light guide 4.

FIG. 15 schematically illustrates an embodiment of shaped illuminationdevice 900 that includes a second linear LED source 101 that isoptically coupled to opposing edge 14 of light guide 4. LED source 101may have an identical structure to that of light source 10 and mayinclude one or multiple LEDs 102 and opaque housing 150 encasing LED(s)102 from three sides, as illustrated in FIG. 15. Accordingly, thestructure of FIG. 15 has a symmetrical configuration in which light cantravel in either direction and can be propagated, extracted and recycledsymmetrically, in accordance with the principles described above forasymmetrical configurations of device 900.

FIG. 16 schematically illustrates an embodiment of shaped illuminationdevice 900 in which both light guide 4 and reflector 30 have a greatercurvature compared to those of FIG. 2 and which is characterized by bendangle β of about 90° (the tangent planes at opposing edges 12 and 14being perpendicular to each other). FIG. 17 schematically illustrates anembodiment in which light guide 4 and reflector 30 have a variablecurvature in a transversal cross-section that is perpendicular to lightinput edge 12. FIG. 18 schematically illustrates an embodiment of shapedillumination device 900 in which light guide 4 and reflector 30 bothhave a substantially planar section adjacent to light input edge 12.

FIG. 19 schematically illustrates an embodiment of shaped illuminationdevice 900 which is formed by two symmetrical sections, such as those ofFIG. 17, for example. Each section is formed by its own linear lightsource 10, curved light guide 4 and similarly curved concave reflector30. The resulting configuration may have the shape of a symmetricallinear trough which emits light from its concave surface. Suchlight-emitting trough may be configured to emit light substantially fromits entire concave area (except a relatively narrow spacing area betweenthe symmetrical sections and may be characterized by a full emissionangle Ω which is less than 180°. According to different embodiments,angle Ω can be approximately 160°, 140°, 120°, 105°, and 90°. Accordingto one embodiment, angle Ω is between 90° and 160°. According to oneembodiment, angle Ω is between 105° and 140°.

According to one embodiment, light guides 4 of symmetrical device 900 ofFIG. 19 may be detached from each other and separated by a spacingdistance. Such distance may be selected to accommodate respective linearlight sources 10 and any accompanying structural members. According toone embodiment, a single central structural support member 58 isprovided. Each linear light source 10 is represented by an LED stripattached to the respective side of central structural support member 58.

Two or more linear light sources 10 may also be replaced by a singlelinear light source configured to emit light into opposing directions(e.g., a fluorescent tube or linear LED strip with side-emittingoptics). According to one embodiment, light guides 4 may joined togetherat their edges and form a single sheet-form light-guiding body. Portionsof light input edges 12 of the respective light guides 4 may be curvedor otherwise shaped to facilitate light coupling from one or more linearlight sources 10.

Shaped illumination device 900 may further include various additionallight shaping layers or films. According to one embodiment, shapedillumination device 900 may include a light diffusing sheet of atransmissive type. Such light diffusing sheet may be curved to the sameshape as light guide 4 and positioned adjacent to concave light outputsurface 20. The light diffusing sheet may also be planar or curved to adifferent shape than light guide 4. A transmissive light diffusing sheetmay also be provided on the side of convex surface 40.

In one embodiment, shaped illumination device 900 includes a brightnessenhancement film disposed on top of surface 20 of light guide 4. Suchbrightness enhancement film may be formed, for example, by amicroprismatic film having isosceles right-angle linear microprismsdistributed over its surface and facing away from light guide 4. Thebrightness enhancement film may be configured to trap and recycle lightemerging from curved light guide 4 and result in a more collimated lightoutput from the device.

Either symmetrical or asymmetrical configurations of shaped illuminationdevice 900 may be used for making various types of lighting fixtures. Anexemplary embodiment of one such type of lighting fixture employing asymmetrical configuration of the device is schematically illustrated inFIG. 20, which shows a suspended downlight 1200 having an invertedtrough configuration. FIG. 21, FIG. 22 and FIG. 23 schematically depicta section view, a top view and a bottom view of downlight 1200,respectively.

Downlight 1200 includes two independently operating arms (sections) ofshaped illumination device 900 each having its own light guide 4,reflector 30, and linear source 10. Each of the linear light sources 10is formed by a strip of LEDs 2 extending parallel to the respectivelight input edge 12. Light sources 10 and respective edges 12 of lightguides 4 are enclosed into a housing 800 that is preferably opaque andmay be configured to block stray light emerging from the light inputareas. Light sources 10 may also be mounted to one or more rigidstructural bars or profiles. By way of example, an extruded profilesimilar to profile 50 shown in FIG. 2. Profile 50 may also be modifiedto support and/or encase both of light sources 10 of downlight 1200. Itmay further include ribs or fins to increase its surface area andpromote heat dissipation from LEDs 2.

Housing 800 may have any suitable color, such as, for example, black,white, gray, bronze, etc. A dark color, including black, may be used,for example to enhance the effect of stray light blocking. According toone embodiment, housing 800 is painted in white color or otherwise madehighly reflective, e.g., by mirroring or white powder coating. Suchhousing 800 may be configured to assist in recycling light within thecavity formed by the trough-shaped downlight (e.g., by reflecting lightexiting from edges 12 back to light guide 4) and/or mask the appearanceof the housing.

Downlight 1200 further has one or more pendant suspension elements 302used to attach the lighting fixture to an overhead structure, such as aceiling. Each suspension element 302 may be exemplified by a pipe, whichmay also be configured to carry wiring within its hollow body, or one ormore cables, chains, etc.

Reflector 30 may be formed from a sheet metal material. It may be bentto the prescribed curved shape and mirrored or coated with a diffuse orsemi-specular light reflecting material (e.g., white paint or powdercoat). Light guide 4 may be formed from a highly transmissive plasticmaterial, such as, for example, acrylic or polycarbonate. Light guide 4may be formed from an optically transmissive sheet that may beoriginally planar. Such optically transmissive sheet may be formed tothe prescribed curved shape using heat, for example. Alternatively, theoptically transmissive sheet may be made sufficiently thin and flexiblesuch that it can be be elastically bent to conform to the shape of morerigid reflector 30. In a yet further alternative, either one or bothreflector 30 and light guide 4 may be formed in an elastic deformationregime by applying a flexing stress and fixing a prescribed shape bystiffening ribs or other suitable means. The prescribed curved shape mayalso be obtained by providing a sufficiently low thickness for lightguide 4 and reflector 30 such that the light guide 4 and reflector 4could bend under their own weight (gravity-assisted bending). Suchexemplary configurations of downlight 1200 may be operated while lightguide 4 and/or reflector 30 are in an elastically bent, strained state.

A method of making shaped edge-lit illumination device 900 may includeproviding elongated light source 10 (i.e., a fluorescent tube or a stripof LEDS 2), providing light guide 4 in the form of a flexible sheet ofan optically transmissive material (such as glass, PMMA, polycarbonate,or the like), providing reflector 30 in the form of a sheet of areflective material, a step of forming light extracting features in theflexible sheet, a step of bending the flexible sheet to a predefinedcurved shape (e.g., at a bend angle sufficient to effectuate lightrecycling), a step of bending the sheet of a reflective material to thesame curved shape, a step of positioning the curved reflective sheetadjacent to a convex surface of the curved light guide 4, and a step ofoptical coupling the elongated light source 10 to a straight edge ofcurved light guide 4. The method may optionally include a step ofpartially enclosing the elongated light source 10 into an opaque housing(e.g., such as housing 800).

According to one embodiment, downlight 1200 may include light guide 4only and no reflector 30. In this case, downlight 1200 may be configuredfor direct and indirect lighting by emitting light both downwards andupwards. Such configuration may be advantageously selected, for example,when downlight 1200 is suspended below a high-reflectance ceiling.According to different embodiments, proportions between light energyemitted downwards and upwards or vice versa may be 50%/50%, 60%/40%,70%/30%, 80%/20%, and 90%/10%.

It may be appreciated that the embodiments of downlight 1200 describedabove may allow for maximizing the light emitting area while maintaininga relatively low profile of the light fixture and eliminating additionalcomponents which may be unwanted in some applications. For instance, theinterior of the trough-shaped body of downlight 1200 may be madesubstantially free from any bulky parts/components or major protrusions.In one embodiment, housing 800 protrudes into the trough cavity abovesurface 20 by no more than 30% of a depth of the trough, more preferablyby no more than 20%, even more preferably by no more than 15%, and stilleven more preferably by no more than 10%. According to differentembodiments, the interior of the trough-shaped body of downlight 1200 issubstantially free from any objects that protrude by more than 10% of adepth of the respective trough and have a transversal size (in a planeperpendicular to a longitudinal axis of the trough) that is greater than20%, 15%, 10%, and 5% of a width of the trough.

FIG. 24 schematically depicts an embodiment of a wall-mounted lightingfixture 1210 employing shaped illumination device 900 in an asymmetricconfiguration. Lighting fixture 1210 is mounted to a wall 370 and isconfigured to emit a soft, divergent light beam from the entire concavebroad-area surface (surface 20) while limiting the angular spread of theemitted light to only functional directions (e.g., downward only and/orgenerally away from wall 24) and hiding the light source from the directview. Lighting fixture 1210 may optionally include a wall reflector 372configured to receive and reflect stray light emitted towards wall 370.

Further details of a structure and different modes of operation ofshaped edge-lit illumination devices shown in the drawing figures aswell as their possible variations and uses will be apparent from theforegoing description of preferred embodiments. Although the descriptionabove contains many details, these should not be construed as limitingthe scope of the invention but as merely providing illustrations of someof the presently preferred embodiments of this invention. Therefore, itwill be appreciated that the scope of the present invention fullyencompasses other embodiments which may become obvious to those skilledin the art, and that reference to an element in the singular is notintended to mean “one and only one” unless explicitly so stated, butrather “one or more.”

Any numerical range recited herein is intended to include all sub-rangessubsumed therein. For example, a range of 1 to 10 is intended to includeall sub-ranges between and including the recited minimum value of 1 andthe recited maximum value of 10, that is, having a minimum value equalto or greater than 1 and a maximum value of equal to or less than 10,such as, for example, 3 to 6 or 2.5 to 8.5. Any maximum numericallimitation recited herein is intended to include all lower numericallimitations subsumed therein and any minimum numerical limitationrecited in this specification is intended to include all highernumerical limitations subsumed therein. Accordingly, Applicant reservesthe right to amend this specification, including the claims, toexpressly recite any sub-range subsumed within the ranges expresslyrecited herein. All such ranges are intended to be inherently describedin this specification such that amending to expressly recite any suchsubranges would comply with the requirements of 35 U.S.C. § 112, firstparagraph, and 35 U.S.C. § 132(a). Also, unless otherwise indicated, allnumerical parameters are to be understood as being prefaced and modifiedin all instances by the term “about”, in which the numerical parameterspossess the inherent variability characteristic of the underlyingmeasurement techniques used to determine the numerical value of theparameter.

All structural, chemical, and functional equivalents to the elements ofthe above-described preferred embodiments that are known to those ofordinary skill in the art are expressly incorporated herein by referenceand are intended to be encompassed by the present claims. Moreover, itis not necessary for a device or method to address each and everyproblem sought to be solved by the present invention, for it to beencompassed by the present claims. Furthermore, no element, component,or method step in the present disclosure is intended to be dedicated tothe public regardless of whether the element, component, or method stepis explicitly recited in the claims. No claim element herein is to beconstrued under the provisions of 35 U.S.C. 112, sixth paragraph, unlessthe element is expressly recited using the phrase “means for.”

Any incorporation by reference of documents above is limited such thatno subject matter is incorporated that is contrary to the explicitdisclosure herein. It is noted that, where a definition or use of a termin a reference, which is incorporated by reference herein isinconsistent or contrary to the definition of that term provided herein,the definition of that term provided herein applies and the definitionof that term in the reference does not apply. Any incorporation byreference of documents above is further limited such that no claimsincluded in the documents are incorporated by reference herein. Anyincorporation by reference of documents above is yet further limitedsuch that any definitions provided in the documents are not incorporatedby reference herein unless expressly included herein. In the event ofinconsistent usages between this document and those documents soincorporated by reference, the usage in the incorporated reference(s)should be considered supplementary to that of this document; forirreconcilable inconsistencies, the usage in this document controls.

What is claimed is:
 1. A suspended lighting fixture for direct/indirectlighting, comprising: a thin curved sheet of an optically transmissivematerial having a concave broad-area surface, an opposing convexbroad-area surface extending parallel to the concave broad-area surface,a first edge, and an opposing second edge; an elongated heat dissipatingstructural element longitudinally extending along the first edge; aplurality of interconnected LED sources arranged into an LED strip andoptically coupled to the first edge, wherein the LED strip is attachedto the structural element; an opaque elongated housing at leastpartially enclosing the LED strip; a plurality of forward-deflecting orforward-scattering light extraction elements formed in or on at leastone of the concave and convex broad-area surfaces and distributed overan area of the curved sheet according to a two-dimensional pattern; andone or more suspension elements configured for suspending the lightingfixture with a downward orientation of the concave broad-area surface;wherein at least some of the plurality of forward-deflecting orforward-scattering light extraction elements are configured to extractlight from the curved sheet and distribute the extracted light from boththe concave and convex broad-area surfaces.
 2. A suspended lightingfixture as recited in claim 1, wherein a first portion of the curvedsheet is disposed in energy receiving relationship with a second portionof the curved sheet and configured to receive light on a concave surfaceand transmit the received light to exit from an opposing convex surface.3. A suspended lighting fixture as recited in claim 1, wherein a concavesurface portion of the curved sheet disposed near the first edge isconfigured to emit at least some light towards the second edge.
 4. Asuspended lighting fixture as recited in claim 1, wherein a surfaceportion of the curved sheet disposed near the first edge is configuredat an angle of peak luminance of greater than 60°.
 5. A suspendedlighting fixture as recited in claim 1, comprising a second plurality ofinterconnected LED sources arranged into a second LED strip, a secondelongated heat dissipating structural element, and a second opaqueelongated housing at least partially enclosing the second LED strip,wherein the second plurality of interconnected LED sources is attachedto the second elongated heat dissipating structural element andoptically coupled to the second edge.
 6. A suspended lighting fixture asrecited in claim 1, wherein at least one of the suspension elementscomprises one or more cables or chains, wherein at least one of saidlight extraction elements defines a surface structure having a totalvolume between 1000 cubic micrometers and 500000 cubic micrometers, asize between 20 to 200 micrometers, and an irregular shape.
 7. Asuspended lighting fixture as recited in claim 1, wherein at least oneof the suspension elements comprises a pipe configured to carry wiringwithin a hollow body.
 8. A suspended lighting fixture as recited inclaim 1, wherein at least some of the plurality of forward-deflecting orforward-scattering light extraction elements are formed by discretesurface relief features separated from each other by smooth portions ofthe concave or convex broad-area surfaces.
 9. A suspended lightingfixture as recited in claim 1, wherein in at least one of the lightextraction elements is configured to extract light from the concavebroad-area surface at a first location of the curved sheet and direct atleast a portion of the extracted light toward a second location of thecurved sheet that is distant from said first location, wherein thecurved sheet is configured to receive the extracted light on the concavebroad-area surface at the second location and propagate the receivedlight to exit from the convex broad-area surface.
 10. A suspendedlighting fixture as recited in claim 1, wherein the curved sheet isconfigured at a bend angle greater than 45° and less than 90°.
 11. Asuspended lighting fixture as recited in claim 1, wherein the curvedsheet is configured at a bend angle greater than 30° and less than 90°.12. A suspended lighting fixture as recited in claim 1, wherein thecurved sheet is configured at a bend angle greater than 90° and lessthan 180°.
 13. A suspended lighting fixture as recited in claim 1,wherein at least a portion of the concave broad-area surface of thecurved sheet is configured at an off-axis surface luminance that isgreater than an on-axis surface luminance at least by a factor of 1.2.14. A suspended lighting fixture as recited in claim 1, wherein thecurved sheet is configured to distribute 40% of light upward and 60% ofthe light downward.
 15. A suspended lighting fixture as recited in claim1, wherein the curved sheet is configured to distribute light upward anddownward in approximately equal proportions.
 16. A suspended lightingfixture as recited in claim 1, wherein the curved sheet is configured todistribute light upward and downward in unequal proportions.
 17. Asuspended lighting fixture as recited in claim 1, comprising a diffusereflector conformably covering at least a portion of the convexbroad-area surface.
 18. A suspended lighting fixture for direct/indirectlighting, comprising: a first curved sheet of an optically transmissivematerial having a first light input edge; a second curved sheet of anoptically transmissive material being symmetrically disposed withrespect to the first curved sheet to cooperatively form a trough-shapedstructure and having a second light input edge facing the first lightinput edge; an elongated heat dissipating structural element positionedbetween the first and second curved sheets; a first strip of LEDsattached to a first longitudinal side of the structural element andoptically coupled to the first light input edge; a second strip of LEDsattached to an opposing second longitudinal side of the structuralelement and optically coupled to the second light input edge; an opaqueelongated housing at least partially enclosing the first and secondstrips of LEDs; a first plurality of light extraction elements formed inor on a first surface of the first curved sheet and distributed over thefirst surface according to a first two-dimensional pattern; a secondplurality of light extraction elements formed in or on a second surfaceof the second curved sheet and distributed over the second surfaceaccording to a second two-dimensional pattern; and one or moresuspension elements configured to retain the trough-shaped structure ina downward orientation; wherein at least some of the first plurality oflight extraction elements are configured to distribute light from twoopposing broad-area surfaces of the first curved sheet, wherein at leastsome of the second plurality of light extraction elements are configuredto distribute light from two opposing broad-area surfaces of the secondcurved sheet, and wherein the trough-shaped structure is configured todistribute a smaller portion of total emitted light upward and a largerportion of the total emitted light downward.
 19. A suspended lightingfixture as recited in claim 18, wherein at least one of the lightextraction elements is formed by one or more discrete forward-deflectingor forward-scattering surface relief features and wherein at least aportion of the a light emitting surface of the first curved sheet isconfigured at an off-axis surface luminance that is greater than anon-axis surface luminance at least by a factor of 1.2.
 20. A suspendedlighting fixture for direct/indirect lighting, comprising: a firstcurved sheet of an optically transmissive material having a first lightinput edge; a second curved sheet of an optically transmissive materialbeing symmetrically disposed with respect to the first curved sheet tocooperatively form a trough-shaped structure and having a second lightinput edge disposed parallel to the first light input edge; an elongatedheat dissipating structural element joining the first and second curvedsheets; a first strip of LEDs attached to the structural element andoptically coupled to the first light input edge; a second strip of LEDsattached to the structural element and optically coupled to the secondlight input edge; an opaque elongated housing at least partiallyenclosing the first and second strips of LEDs; a first plurality oflight extraction elements formed in or on a first surface of the firstcurved sheet and distributed over the first surface according to a firsttwo-dimensional pattern; a second plurality of light extraction elementsformed in or on a second surface of the second curved sheet anddistributed over the second surface according to a secondtwo-dimensional pattern; and one or more suspension elements configuredto suspend the lighting fixture with a downward orientation of thetrough-shaped structure; wherein at least some of the first plurality oflight extraction elements are configured to extract light from twoopposing broad-area surfaces of the first curved sheet, wherein at leastsome of the second plurality of light extraction elements are configuredto extract light from two opposing broad-area surfaces of the secondcurved sheet, and wherein the lighting fixture is configured todistribute a smaller portion of light upward and a larger portion of thelight downward.
 21. A suspended lighting fixture as recited in claim 20,wherein the trough-shaped structure is configured to distribute 40% oflight upward and 60% of the light downward.
 22. A suspended lightingfixture as recited in claim 20, comprising a first reflector covering asurface of the first curved sheet and a second reflector covering asurface of the second curved sheet.
 23. A suspended lighting fixture asrecited in claim 20, wherein both the first and second curved sheets areconfigured to emit light at an off-axis surface luminance which isgreater than an on-axis surface luminance at least by a factor of 1.2.24. A suspended lighting fixture as recited in claim 20, wherein each ofthe first and second curved sheets is configured to distribute lightupward and downward in approximately equal proportions.
 25. A suspendedlighting fixture as recited in claim 20, wherein at least one of thelight extraction elements comprises a surface relief feature formed by aforward-scattering material, and wherein a surface density of the lightextraction elements increases with a distance to elongated heatdissipating structural element.
 26. A suspended lighting fixture asrecited in claim 20, wherein the first curved sheet is configured toemit light from an edge which is opposite to the first light input edgeand wherein the second curved sheet is configured to emit light from anedge which is opposite to the second light input edge.